How to solve - The SqlParameterCollection only accepts non-null Microsoft.Data.SqlClient.SqlParameter type objects, not System.Data.SqlClient.SqlParameter objects.' - Error in .Net

 The error message System.InvalidCastException: "The SqlParameterCollection only accepts non-null Microsoft.Data.SqlClient.SqlParameter type objects, not System.Data.SqlClient.SqlParameter objects" occurs when you try to add a System.Data.SqlClient.SqlParameter object to a Microsoft.Data.SqlClient.SqlParameterCollection object.

This error occurs because the Microsoft.Data.SqlClient and System.Data.SqlClient namespaces represent two different ADO.NET providers for SQL Server, and the two providers use different types for their SQL parameters.

To fix this error, you need to make sure that you use the correct type of SQL parameter object when you are working with a Microsoft.Data.SqlClient.SqlParameterCollection. If you are using Microsoft.Data.SqlClient, you should use Microsoft.Data.SqlClient.SqlParameter objects. If you are using System.Data.SqlClient, you should use System.Data.SqlClient.SqlParameter objects.

Here's an example of how to create a Microsoft.Data.SqlClient.SqlParameter object and add it to a Microsoft.Data.SqlClient.SqlParameterCollection object:

c#
using Microsoft.Data.SqlClient;

// create a SqlConnection object
using SqlConnection connection = new SqlConnection("your_connection_string_here");

// create a SqlCommand object
using SqlCommand command = new SqlCommand("SELECT * FROM MyTable WHERE MyColumn = @param1", connection);

// create a SqlParameter object and add it to the SqlCommand's parameters collection
SqlParameter parameter = new SqlParameter("@param1", SqlDbType.NVarChar, 50);
parameter.Value = "my_parameter_value";
command.Parameters.Add(parameter);

Note that in this example, we are using the Microsoft.Data.SqlClient.SqlParameter object instead of the System.Data.SqlClient.SqlParameter object, since we are working with a Microsoft.Data.SqlClient.SqlParameterCollection object.